1. Field of the Invention
The present invention relates to an illumination device, an image pickup system, a film holder, a light emission control device, and a light emission control method, and more particularly to control executed when an optical accessory that changes color characteristics of light transmitted therethrough is attached forward of a light emission section of the illumination device.
2. Description of the Related Art
In general, in an illumination device used for a camera, such as a strobe device (hereinafter simply referred to as the strobe), a discharge tube, such as a xenon tube, is used as a light source of the illumination device. A color temperature of light (strobe flash light) emitted from the strobe using a xenon tube is set to a value in the vicinity of the temperature of sunlight (6000K). For this reason, if shooting is performed using the strobe under an environment having a color temperature different from the color temperature set as above, a photographed image sometimes has unnatural colors.
To eliminate this problem, there has been proposed a technique in Japanese Patent Laid-Open Publication No. 2009-20298, in which a filter holder to which an optical accessory, such as a color filter, is attached is mounted forward of a light emission section of the strobe to thereby change the color temperature of light emitted from the strobe. In the technique disclosed in Japanese Patent Laid-Open Publication No. 2009-20298, identification information for identifying a color filter type is added to the color filter side, and a reading section provided on the strobe side reads the identification information of the color filter to thereby identify the type of the color filter attached to the filter holder. Then, the strobe determines the color temperature of the emitted light according to the identified color filter type, and displays the color temperature information on a display section, or transmits the same to the camera on which the strobe is mounted.
On the other hand, there has been proposed a technique in which a light emission amount measured when the strobe is caused to emit light is stored in a memory as reference data, and when controlling the amount of light emitted from the strobe during shooting, light emission amount control is performed according to the reference data read out from the memory (see Japanese Patent Laid-Open Publication No. H09-61903). In the light emission amount control mentioned as above, the strobe flash light is received by a photometry sensor, and when an integrated value obtained by integrating the outputs from the photometry sensor reaches a predetermined value, light emission is stopped.
By the way, when the optical accessory that changes color characteristics of light transmitted therethrough is attached forward of the light emission section, not only the color temperature of the emitted light is converted but also a phenomenon that the emitted light is attenuated occurs. In an image pickup apparatus on which the strobe is mounted, preliminary light emission is performed before the main light emission from the strobe to thereby acquire information on an object (object information) for use in calculation of the main light emission amount.
Therefore, when the optical accessory is attached to the strobe, if attenuation information indicative of attenuation in the amount of emitted light due to attachment of the optical accessory is not acquired by the image pickup apparatus, the main light emission amount is calculated according to the erroneous object information, which sometimes results in acquisition of an inappropriate amount of main light emission.
Next, the problem in shooting with the above-described insufficient light emission amount will be described in detail. When a color filter is attached to the strobe, the amount of actually emitted light is reduced due to the following factor, which may prevent shooting from being performed with a desired light amount.
Now, the factor which reduces the light emission amount when the color filter is attached will be generally described with reference to FIGS. 26A, 26B, and 27.
FIGS. 26A and 26B are views useful in explaining the light emission section of the strobe, in which FIG. 26A shows a state in which the color filter is not attached forward of the light emission section of the strobe, and FIG. 26B shows a state in which the color filter is attached forward of the light emission section of the strobe.
The light emission section includes an xenon tube 11 as a light source, and a photometry sensor 30 which receives light from the xenon tube 11, and monitors an amount of light emitted from the xenon tube 11. A Fresnel panel 64 is disposed forward of the xenon tube 11 (in the direction of emitting light from the light emission section) and this Fresnel panel 64 causes the strobe flash light emitted from the xenon tube 11 to be irradiated in a uniformly spread manner. Further, in FIG. 26B, a color filter 401 is attached forward of the Fresnel panel 64.
Now, when strobe flash light 600 is emitted from the xenon tube 11, part of the strobe flash light 600 is reflected by the Fresnel panel 64, and goes to the photometry sensor 30 as Fresnel reflected light 700. Further, as shown in FIG. 26B, part of the strobe flash light 600 is reflected by the color filter 401, and goes to the photometry sensor 30 as color filter reflected light 800.
Therefore, by attaching the color filter 401 forward of the light emission section, the amount of light which enters the photometry sensor 30 when the xenon tube 11 is caused to emit light increases by an amount of the filter reflected light 800.
FIG. 27 is a diagram showing changes in the integrated value obtained by integrating the outputs from the photometry sensor 30 appearing in FIGS. 26A and 26B.
In FIG. 27, a broken line indicates a light emission waveform of the strobe flash light, and a light emission amount integrated value (DEF) indicates the integrated value in the case where the color filter 401 is not attached forward of the light emission section. Further, a light emission amount integrated value (FIL) indicates the integrated value in the case where the color filter 401 is attached forward of the light emission section. Note that FIG. 27 shows a state in which the light emission section is caused to emit light at the maximum output level.
As shown in FIG. 27, when the color filter 401 is attached, the amount of light received by the photometry sensor 30 increases by the amount of the filter reflected light, and as a result, the light emission amount integrated value (FIL) is larger than the light emission amount integrated value (DEF). As a consequence, the light emission amount integrated value (FIL) reaches the predetermined value earlier than the light emission amount integrated value (DEF), and in the state in which the color filter 401 has been attached, the light emission is controlled to stop before reaching a desired light emission amount. As a result, when the color filter 401 is attached, shooting is executed in a state in which a desired light emission amount cannot be obtained, which sometimes prevents a good image from being obtained.